1. Field of the Invention
The present invention relates to a vehicle-seat reclining device, and a production method therefor.
2. Description of the Related Art
U.S. Pat. No. 6,010,191 discloses a vehicle-seat reclining device. The vehicle-seat reclining device includes a seat cushion frame, a seat back frame, and a lock mechanism provided between the seat cushion frame and the seat back frame. The lock mechanism includes a lower housing fixed to the seat cushion frame, an upper housing fixed to the seat back frame, and functional components that switch between states in which the rotation of the upper housing relative to the lower housing is prevented and allowed. Therefore, the lock mechanism also switches between states in which the pivotal movement of the seat back frame relative to the seat cushion frame is prevented and allowed.
The seat cushion frame and the lock mechanism (lower housing) are fixedly connected by fitting a plurality of fitting projections of the lower housing in a plurality of corresponding fitting holes of the seat cushion frame, and by welding fitting portions therebetween. Such a connection manner using a fitting technique is adopted to ensure a sufficient connecting strength.
In the vehicle-seat reclining device disclosed in the above publication, since a plurality of fitting projections project from the lower housing, it is necessary to provide space for the fitting projections. Moreover, in order to ensure the connecting strength, it is necessary to place the fitting projections, which are fitted in and welded to the fitting holes, at a distance in accordance with the required strength from the center of rotation of the lower housing. This increases the diameter of the lower housing, and also increases the total size of the reclining device.
U.S. Pat. No. 6,390,556 discloses another vehicle-seat reclining device that ensures the strength of connection by using a fitting technique. In this vehicle-seat reclining device, a seat back frame and a lock mechanism are connected by fitting a gear-shaped fitting portion, which is provided on the outer periphery of a disc-shaped side plate in the center of the lock mechanism, in a corresponding fitting hole provided in the seat back frame, and by welding the fitting portion and the fitting hole. In this method, however, the fitting portion projects from the center of the lock mechanism only for connection, and at least a space for the fitting portion is needed.